Devices and methods for delivery of desired components to a site of interest remain a growing need. A variety of methods and routes of administration have been developed to deliver pharmaceuticals or diagnostics, such as small molecular drugs, imaging agents and/or other biologically active compounds (e.g., peptides, hormones, proteins, and enzymes) and many routes of administration are known for delivering desired pharmaceuticals to a patient. However, as greater knowledge is learned regarding toxicity of drugs and the ability to elicit specific responses by delivery of a pharmaceutical only to a specific portion of the body, controlled release of pharmaceuticals after their administration has become a highly important area of research.
For example, the therapeutic efficacy of active agents is often limited by the inability to selectively deliver the drugs to the cell, e.g., most of the currently available anticancer drugs are highly cytotoxic and can kill normal cells along with cancerous cells. Thus, when high doses of drugs are used, there can be severe side effects. As a result, most of the currently used anticancer drugs have a rather limited therapeutic index. Such a limit on dosage can prevent complete eradication of cancer cells in a patient, and may lead to recurrence of the cancer in many patients. The limit in dosage can also predispose the recurring cancer to drug resistance, thus worsening the prognosis for the patient.
More generally, technologies which can specifically deliver drugs to affected tissues in diseases involving viral, bacterial, inflammatory, metabolic, and neurologic imbalances represent an important therapeutic breakthrough. Often, therapeutics for these diseases very strictly requires a large therapeutic window to be considered for clinical study. Introduction of moieties which deliver these therapeutics directly and specifically to the diseased tissues or to the disease-causing agents lowers the specificity requirements of the therapeutic itself. Accordingly, there is an ongoing need for new therapeutic approaches that permit the selective delivery of active agents to diseased cells, thereby providing improved therapeutic indices.